This invention concerns methods and products utilizing fibrous absorbent bodies for absorbing fluids. In particular, the invention concerns products such as catamenial tampons, diapers, sanitary napkins and the like and is specifically directed toward fibrous absorbent bodies which are easily handled in processes for manufacturing such products and which maintain their integrity when wet with body fluids.
The vast majority of body fluid absorbent products now in use comprise, at least in their formative stages, pads of loosely associated fibrous, and generally cellulosic, absorbent materials such as comminuted wood pulp fluff, rayon staple, cotton, cotton linters and the like. For generations, these materials have proven to be useful and effective in dressings, diapers and sanitary protection devices in that such materials are absorbent, inexpensive, and, in the case of absorbent products which must be worn by the user for substantial periods of time, such materials are flexible and comfortable. Unfortunately, balanced against these highly desirable properties, is the fact that pads manufactured from the loosely associated fibrous materials are relatively weak, having little tensile strength and must be handled gingerly throughout any manufacturing process.
The manufacturing problems associated with these loosely associated fibrous materials has been aggravated to some extent by the desire to incorporate into the body of such fibrous materials certain cellulosic materials (herein termed hydrocolloid) which exhibit substantially increased absorptive properties by virtue of chemical modification. Examples of such materials are the grafted cellulosic copolymers described in U.S. Pat. No. 3,889,678 issued to Pronoy Chatterjee, et al. on June 17, 1975; and the cross-linked carboxyalkyl cellulosic materials described in U.S. Pat. Nos. 3,731,686 and 3,858,585 issued to Pronoy Chatterjee on May 8, 1973 and June 7, 1975; and in U.S. Pat. No. 3,589,364 issued to W. L. Dean, et al. on June 29, 1971. These hydrocolloidal materials are in the form of highly swellable and highly retentive fibers. It is desirable to combine these fibers with the more conventional absorbent materials such as rayon, woodpulp, cotton or the like to produce an absorbent body having increased fluid retentive properties. Unfortunately, when mixing such fibrous materials, it is not an easy processing task to get an even distribution and this adds to the burden of producing an absorbent body for the products of interest herein.
In my copending U.S. patent application Ser. No. 82,400, filed Oct. 5, 1979, I describe a method for avoiding the difficulty of handling such materials and specifically describe a method whereby the materials are formed into a board and the board is rendered flexible by virtue of being dry compressed after its formation. While this method has indeed allowed the use of fibrous systems in a more readily processible form and produces products which are comfortable to the user, there are still drawbacks associated with this product. Specifically it has been found that when boards of fibrous systems incorporating such chemically modified fibers as those described above become wet with body fluids such as urine or menstrual fluid, the boards deform greatly, particularly under the influence of pressures common in the use of products such as tampons, diapers and the like. Under the influence of pressures exerted by the wearer in normal use of such products, the boards tend to collapse, flow and deform thereby greatly reducing their abilities to trap fluids in the interstices between the fibers and allow the penetration of additional fluid. Said in other words, the deformation tends to block the ability of fluid to penetrate and hence fully utilize the absorbent capacities of these absorbent, board-like materials.
Accordingly, there is a need for producing a densified board-like absorbent material which can be readily handled during processing, which is comfortable when incorporated in absorbent products worn by the user, and which will resist deformation when subjected to pressure in the wet state.